1. Field of the Invention
The present invention relates to a scintillator, radiation detection apparatus, and manufacturing methods thereof.
2. Description of the Related Art
Recently, radiation detection apparatuses have been put into practical use, in which a photoelectric conversion substrate having an array of photoelectric conversion elements and a scintillator for converting radiation such as an X-ray into light with a wavelength detectable by the photoelectric conversion elements are stacked. As scintillators, for example, a scintillator made of an alkali halide material typified by a material prepared by doping Tl in CsI, and a scintillator made of a material prepared by doping Tb in GdOS are mainstream. Particularly, when vacuum deposition is performed using an alkali halide material, columnar crystals grow. However, the alkali halide material is highly deliquescent, so the scintillator needs to be covered with a highly moisture-proof protection structure.
Japanese Patent Laid-Open No. 2008-261651 discloses a method of suppressing decreases in the sensitivity and sharpness of a radiation detection apparatus by preventing entry of a protection layer resin into a scintillator. Japanese Patent No. 4279462 discloses a method of protecting a scintillator from external water vapor by covering the surface of the scintillator with an organic resin, and filling an organic resin in the gaps between columnar crystals forming the scintillator.
The alkali halide scintillator has gaps between columnar crystals. In the scintillator having the structure as disclosed in Japanese Patent Laid-Open No. 2008-261651, entry of a resin into gaps between columnar crystals is suppressed when forming a protection layer. Thus, decreases in sharpness and MTF (Modulation Transfer Function) can be suppressed. However, in the scintillator having the structure as disclosed in Japanese Patent Laid-Open No. 2008-261651, a shock applied to the scintillator is not distributed but is applied to columnar crystals, and the columnar crystals are readily damaged. To the contrary, when an organic resin is filled in the gaps between columnar crystals, as in the scintillator disclosed in Japanese Patent No. 4279462, a shock applied to the scintillator can be distributed. However, in the scintillator disclosed in Japanese Patent No. 4279462, a substance higher in refractive index than vacuum and air exists between columnar crystals. Thus, the refractive index difference between the columnar crystal and the organic resin in contact with it decreases. This impairs the light guiding effect in which light generated in the columnar crystal travels through the columnar crystal, decreasing the sharpness and MTF.